Honda FOURTRAX FOREMAN 4X4 TRX500FM 2009 Owner's Manual page 165

Also, if you hit a pothole or other hard object while riding, stop as soon
as you safely can and carefully inspect the tires for damage.
Tread Wear
Front
Rear
(1) groove depth
(2) wear indicator
To check the condition of a tire tread, measure the groove depth ( ) in
the center of the tire, or check the wear indicator ( ).
For best performance, you should replace a tire before the tread depth at
the center reaches the following limits:
front
rear
(3)
(3) wear indicator
location mark
3/16 in (4 mm)
3/16 in (4 mm)
Servicing Your Honda
Tires
(1)
3/16 in
(4 mm)
NEW
Replace
(2)
2
1
157